1. Field of the Invention
Various embodiments disclosed herein are generally directed to a perpendicular magnetic recording medium including a recording layer having a plurality of regions with different magnetic anisotropy constants and a method of manufacturing the perpendicular magnetic recording medium.
2. Description of the Related Art
Magnetic recording methods may be classified into perpendicular and longitudinal magnetic recording methods. In the longitudinal magnetic recording method, information is recorded by using a characteristic that a magnetization direction of a magnetic layer is aligned in parallel with a surface of the magnetic layer. In the perpendicular magnetic recording method, information is recorded by using a characteristic that a magnetization direction of a magnetic layer is aligned perpendicularly to the surface of the magnetic layer. Regarding the recording density, the perpendicular magnetic recording method is more advantageous than the longitudinal magnetic recording method. Accordingly, in order to obtain high density in magnetic recording, the perpendicular magnetic recording medium has been continuously researched.
FIG. 1 illustrates a general structure of a conventional perpendicular magnetic recording medium. Referring to FIG. 1, the perpendicular magnetic recording medium includes a substrate 10, a soft-magnetic underlayer 12, an intermediate layer 14, and a recording layer 16. A magnetic field generated from a recording head (not shown) passes through the soft-magnetic underlayer 12 and returns to the recording head, thereby forming a magnetic path H. At this time, a perpendicular component of the magnetic field magnetizes magnetic domains of the recording layer 16 and records information.
On the other hand, in magnetic recording, the recording density is limited due to a superparamagnetic effect. That is, as the recording density increases, a grain size of the recording medium decreases. Accordingly, thermal stability decreases. When the thermal stability decreases below a predetermined threshold, magnetic moments may not be aligned in one direction due to thermal agitation. The threshold is represented as follows:
                                                                        K                U                            ⁢              V                                                      K                B                            ⁢              T                                >          40                ,                            [                  Inequality          ⁢                                          ⁢          1                ]            where, KU is a magnetic anisotropy constant, V is a grain volume, KB is the Boltzmann constant, and T is an absolute temperature.
Accordingly, in order to manage the increase of the recording density, the thermal stability that satisfies Inequality 1 has to be maintained. In order to maintain the thermal stability, a magnetic recording medium with a large magnetic anisotropy constant KU has to be manufactured so as to have a high anisotropic energy even in a small grain size. When the anisotropic energy of the recording medium increases, the coercivity Hc of the recording medium necessarily increases. Accordingly, it is difficult that magnetization reversal occurs. Thus, writability becomes low. For example, in order to secure the stability of recorded data for ten years in recording of 1000 Gb/in2, the required magnetic anisotropy constant KU is 1.99E7 erg/cc. However, it is difficult for a current recording head to record data in a magnetic recording medium having a large magnetic anisotropy constant KU. In order to solve this problem, a method of depositing a magnetic thin film having a large magnetic anisotropy constant KU, a magnetic thin film having a small magnetic anisotropy constant KU, and an intermediate layer therebetween by changing the thickness of the intermediate layer has been tried. However, in this case, materials selectable for a recording layer are limited, and thus it is difficult to manufacture a magnetic recording medium by using the aforementioned method. That is, since it is impossible to form the same isolation regions in two different magnetic layers, transition noise increases. Accordingly, the signal to noise ratio (SNR) increases.